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Friday, August 31, 2012

eigrp default-network...

this command does not work alone, nor does it really work at all...

two connected routers, two loopbacks, same AS, eigrp 1...

no default-network, no default route

r1(config)#router eigrp 1
r1(config-router)#netw 1.0.0.0
r1(config-router)#net 172.16.0.0
r1(config-router)#end
r1#
*Aug 31 11:39:02.867: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 172.16.1.2 (FastEthernet0/0) is up: new adjacency
*Aug 31 11:39:04.199: %SYS-5-CONFIG_I: Configured from console by console
r1#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/8/20 ms
r1#

r1#sh ip route | ex L | inc loop
    
Gateway of last resort is not set

      1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        1.1.1.0/24 is directly connected, Loopback0
      2.0.0.0/24 is subnetted, 1 subnets
D        2.2.2.0 [90/156160] via 172.16.1.2, 00:01:18, FastEthernet0/0
      172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C        172.16.1.0/24 is directly connected, FastEthernet0/0

eigrp works as expected...  add a default route to the loopback...

r1(config)#ip route 0.0.0.0 0.0.0.0 lo0   
%Default route without gateway, if not a point-to-point interface, may impact performance
r1(config)#

note above error...

below, note gateway of last resort is set for the local router...

r1#sh ip route | ex L | inc loop
     
Gateway of last resort is 0.0.0.0 to network 0.0.0.0

S*    0.0.0.0/0 is directly connected, Loopback0
      1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        1.1.1.0/24 is directly connected, Loopback0
      2.0.0.0/24 is subnetted, 1 subnets
D        2.2.2.0 [90/156160] via 172.16.1.2, 00:07:10, FastEthernet0/0
      172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C        172.16.1.0/24 is directly connected, FastEthernet0/0

good... but the expected behavior when the ip default-network command is added in global configuration is for default route propagation in the AS...

r1(config)#ip default-netw 1.1.1.0
r1(config)#end

r2 does not get a hit...

r2#sh ip route | excl L | incl loop
     
Gateway of last resort is not set

      1.0.0.0/24 is subnetted, 1 subnets
D        1.1.1.0 [90/156160] via 172.16.1.1, 00:09:12, FastEthernet0/0
      2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        2.2.2.0/24 is directly connected, Loopback0
      172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C        172.16.1.0/24 is directly connected, FastEthernet0/0

take away the default-network command and you lose the candidate static...

add a default network in eigrp...

r1(config)#router eigrp 1
r1(config-router)#netw 0.0.0.0
r1(config-router)#end

r2#sh ip route | excl L | incl loop
     
Gateway of last resort is 172.16.1.1 to network 0.0.0.0

D*    0.0.0.0/0 [90/156160] via 172.16.1.1, 00:00:50, FastEthernet0/0
      1.0.0.0/24 is subnetted, 1 subnets
D        1.1.1.0 [90/156160] via 172.16.1.1, 00:15:18, FastEthernet0/0
      2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        2.2.2.0/24 is directly connected, Loopback0
      172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C        172.16.1.0/24 is directly connected, FastEthernet0/0

would someone please tell me what the command ip default-network in eigrp does except create a candidate static on the local router and give me a big friggin headache...

ip default-network 1.0.0.0


this command also changes nothing...

of course i didn't want someone to get hysterical on me so i did the same exercise with real equipment...

i added a default route between 2 routers and the result was the same... the default showed up in the route table on the local router...

r1#sh ip route                                                                 
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP                 
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area          
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2          
       E1 - OSPF external type 1, E2 - OSPF external type 2                    
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2   
       ia - IS-IS inter area, * - candidate default, U - per-user static route 
       o - ODR, P - periodic downloaded static route                           
                                                                               
Gateway of last resort is 0.0.0.0 to network 0.0.0.0                           
                                                                               
     1.0.0.0/24 is subnetted, 1 subnets                                        
C       1.1.1.0 is directly connected, Loopback0                               
     2.0.0.0/24 is subnetted, 1 subnets                                        
D       2.2.2.0 [90/40640000] via 192.168.100.2, 00:01:17, Serial0/0           
     192.168.100.0/28 is subnetted, 1 subnets                                  
C       192.168.100.0 is directly connected, Serial0/0                         
S*   0.0.0.0/0 is directly connected, Loopback0       

and no gateway as expected...

r2#sh ip route                                                                 
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP                 
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area          
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2          
       E1 - OSPF external type 1, E2 - OSPF external type 2                    
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2   
       ia - IS-IS inter area, * - candidate default, U - per-user static route 
       o - ODR, P - periodic downloaded static route                           
                                                                               
Gateway of last resort is not set                                              
                                                                               
     1.0.0.0/24 is subnetted, 1 subnets                                        
D       1.1.1.0 [90/40640000] via 192.168.100.1, 00:03:55, Serial0/0           
     2.0.0.0/24 is subnetted, 1 subnets                                        
C       2.2.2.0 is directly connected, Loopback0   

then i added the ip default-network command...

r1(config)#ip default-netw 1.0.0.0                                             
r1(config)#end                                                                 
r1#sh i                                                                        
*Jul 22 10:22:22.439: %SYS-5-CONFIG_I: Configured from console by console      
r1#sh ip route                                                                 
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP                 
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area          
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2          
       E1 - OSPF external type 1, E2 - OSPF external type 2                    
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2   
       ia - IS-IS inter area, * - candidate default, U - per-user static route 
       o - ODR, P - periodic downloaded static route                           
                                                                               
Gateway of last resort is 0.0.0.0 to network 0.0.0.0                           
                                                                               
 *   1.0.0.0/24 is subnetted, 1 subnets                                        
C       1.1.1.0 is directly connected, Loopback0                               
     2.0.0.0/24 is subnetted, 1 subnets                                        
D       2.2.2.0 [90/40640000] via 192.168.100.2, 00:05:08, Serial0/0           
     192.168.100.0/28 is subnetted, 1 subnets                                  
C       192.168.100.0 is directly connected, Serial0/0                         
S*   0.0.0.0/0 is directly connected, Loopback0                                
r1#

r2#sh ip route                                                                 
                                                                               
Gateway of last resort is not set                                              
                                                                               
     1.0.0.0/24 is subnetted, 1 subnets                                        
D       1.1.1.0 [90/40640000] via 192.168.100.1, 00:06:26, Serial0/0           
     2.0.0.0/24 is subnetted, 1 subnets                                        
C       2.2.2.0 is directly connected, Loopback0       

of course not...

then i added the network 0.0.0.0 in eigrp on r1 and...

r2#sh ip route                                                            
                                                                        
Gateway of last resort is 192.168.100.1 to network 0.0.0.0                     
                                                                               
     1.0.0.0/24 is subnetted, 1 subnets                                        
D       1.1.1.0 [90/40640000] via 192.168.100.1, 00:07:43, Serial0/0           
     2.0.0.0/24 is subnetted, 1 subnets                                        
C       2.2.2.0 is directly connected, Loopback0      

like magic, the gateway appeared... you can also perform this with redistribution static in eigrp but that yeilds an external route with an AD of 170...

the ip default-network command does not alone propagate a default-network in an eigrp AS...

so there... thanks for ruining my day eigrp...

    
Posted by arteq at Friday, August 31, 2012
Labels: , ,

10 comments:

  1. AnonymousSeptember 15, 2012 at 11:14 AM

    according to your scenario East & West routers, which router is R1 and which one is R2?

    ReplyDelete
  2. arteqSeptember 15, 2012 at 11:17 AM

    does it matter?

    ReplyDelete
    Replies
    1. AnonymousSeptember 16, 2012 at 12:12 PM

      it means tht default-network works with classful networks and if thr r a default route exists.

      Delete
  3. AnonymousSeptember 16, 2012 at 12:14 PM

    Can u tell me tht where we hv to use this default-network command?

    ReplyDelete
  4. arteqSeptember 16, 2012 at 12:20 PM

    exactly, as i stated... that was always only my point... default-network for eigrp will not propagate a default network on it's own... a default network must exist such as ip route 0.0.0.0 0.0.0.0 x.x.x.x, or it can also be propagated using the eigrp network 0.0.0.0 statement, or through redistribution, but not alone... default-network will give you local results only... it does not by itself propagate a default-network... in other words, it does not work like information-originate...

    ReplyDelete
  5. Anu TigerSeptember 16, 2012 at 12:20 PM

    hmmm good.
    it means that if we want to advertise a default route for all routers in our network than this command will be in used?

    ReplyDelete
  6. arteqSeptember 16, 2012 at 12:25 PM

    frankly, i do not know why it is needed other than to add a candidate default route to the local router... better to use ip route 0.0.0.0 0.0.0.0 x.x.x.x, and propagating that to the neighbor using eigrp netwotk 0.0.0.0

    ReplyDelete
  7. arteqSeptember 16, 2012 at 12:38 PM

    do yourself a favor and set up a lab to prove it for yourself...

    ReplyDelete
  8. AnonymousNovember 12, 2012 at 1:22 PM

    I agree, the command is a bag of shite

    ReplyDelete
  9. arteqNovember 12, 2012 at 1:29 PM

    yep...

    ReplyDelete

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